Voltage regulator



P 1, 1953 F. R. MILSOM 2,651,020

VOLTAGE REGULATORS Filed July 23, 1951 F l5 E II D is I02 FIG. I

lOl lOl FIG. 2

lOl IOI C 47 DE 48 F INVNTOR: I02 I02 H FIG 3 fiTwaRNcYs:

Patented Sept. 1, 1953 UNITED STATES PATENT OFFICE VOLTAGE REGULATOR Application July 23, 1951, Serial No. 238,040 In Great Britain July 27, 1950 9 Claims.

The present invention relates to the provision of voltage regulators for alternating current supplies. Previously proposed regulators have had disadvantages in that comparatively simple types of regulators tend to produce a Wave-form with a high harmonic content, necessitating the provision of filter circuits to remove a substantial proportion of the harmonic content if the output is to be used in apparatus where the wave-form is at all critical and also the regulation may not be as good as is desirable, while the types of regulator which produce an output of good waveform and have good regulation tend to be inherently complicated. Furthermore the voltage output of such regulators is usually frequency dependent.

It is therefore the object of the present invention to provide a comparatively simple voltage regulator for an alternating current supply producing an output wave-form of low harmonic content and with good regulation, and in which the output voltage is substantially unaffected by normal frequency variations.

According to the present invention a voltage regulator supplying at a pair of output terminals a voltage of a substantially constant datum amplitude derived from a voltage of variable amplitude at a pair of input terminals comprises means coimected across the output terminals to give a D. C. magnetic flux whose magnitude and sign are in accordance with the variation of the voltage across the output terminals from its datum amplitude, a transformer whose secondary winding is connected between the first input terminal and the first output terminal, said transformer having a centre-tapped primary, the centre tap of the said primary being connected to one of the input terminals, two similar variable impedance elements of the saturable reactor type connected respectively between the other input terminal and the remaining terminals of the transformer primary and means to vary the impedance of the variable impedance elements difierentially in accordance with the aforementioned D. C. magnetic flux, the variation being such that the voltage across the transformer secondary is such as to reduce the variation of the voltage between the output terminals from its datum amplitude.

The means for deriving the D. C. flux may conveniently comprise a bridge the impedance of at least one of whose arms depends upon the voltage across it, one pair of terminals of the said bridge being connected across the output terminals of the regulator and the voltage across the remain- 2 ing (output) pair of terminals being utilised to generate the requisite flux. The voltage across the output terminals of the bridge may be ap plied to the input terminals of a phase sensitive demodulator, the output from which is applied to control the impedances of the saturable reactors. Two opposite arms of the bridge may conveniently be constituted by elements, such as metal filament lamps, whose resistance depends upon the current flowing therein, while the remaining arms constituted by resistive elements Whose resistance is largely independent of the current flowing therein. Alternatively, one pair of adjacent arms may consist of resistive elements while the other adjacent arms consist respectively of an inductor whose inductance is substantially independent of the voltage across it and an inductor whose impedance changes relatively suddenly at a critical value of the voltage across it. Whatever form of bridge is used, it is preferably substantially balanced when the output voltage from the regulator has its datum amplitude.

Alternatively the means for deriving the D. C; flux may comprise a first impedance element whose impedance is substantially independent of the voltage across it in series with a first rectifier connected across the output terminals in parallel with a second impedance element whose impedance varies substantially with the voltage across it in series with a second rectifier also connected across the output terminals together with first and second windings respectively connected across the outputs of said rectifiers and arranged to generate the requisite flux.

Whatever form is used, the means generating the D. C. magnetic flux may be connected across the output terminals either directly or through a transformer; and the saturable reactors are conveniently arranged and controlled as described in British specification No. 633,375.

Voltage regulators constructed in accordance with the present invention will now be described with reference to the accompanying drawings of which:

Figure 1 shows one embodiment of the invention.

Figure 2 shows one alternative form of the means connected across the output terminals responsive to variations in the voltage between them.

Figure 3 shows a second alternative form of these means.

Referring to Figure 1, an unstabilised A. C. input voltage is applied to terminals 5, 2 while a stabilised output voltage is obtained between output terminals it! and H32. Terminals i and I (ll are connected to the secondary winding s of a transformer 13. The primary windin 5 of transformer 3 is centre-tapped and the centretap connected to input terminal l. One of the remaining terminals iii of winding 5 is connected to the common terminal of two similar saturable reactors S, I? the other terminals of the reactors being joined through two similar dry plate rectifiers 8, 8. The other remaining terminal is connected to two further similar reactors iii, H associated with similar dry plate rectifiers i2, it. The junctions of rectifiers 8, s and i2, 53 are both connected to terminal 2. The effective impedances of windings 5, '5, iii, H are controlled by direct current flowing in control windings i l and lo, the impedance between terminal 5! and terminal 2 being increased and that between terminal 52 and terminal 2 being decreased for one direction of resultant flux produced by i5, i5, and vice versa for other. The precise arrangement and operation of windings 6, "i, l9, i i, I i, l5 and their associated iron cores is fully described in British specification No. 633,375 and will not be further discussed here.

The primary winding is of a transformer 29 is connected between the output terminals iiil and $552, while the secondary ii is connected to one pair of opposite terminals of a bridge l8 having in one pair of opposite metal filament lamps 59, 2E and in the other pair resistors 72 i, 22, resistor 2i being variable. The other pair of opposite terminals is connected to the input terminals A, B, of a phase-sensitive demodulator 23, consisting of resistors and dry plate rectifier elements arranged in a conventional manner. The carrier input to the demodulator (at terminals 2i, 28) is obtained from the secondary it of a transformer 24 whose primary 25 is connected between terminals lei, M2. The output from demodulator 23 is connected to terminals C, D, of control winding it. As is Well known the resistance of metal filament lamps such as l9, 2%) varies rapidly with temperature and hence with the current flowing throuqh them. The bridge 23 is so arranged that when the voltage between terminals iill I02 is that desired, the bridge i8 is balanced. When the volt age deviates from the desired datum a voltage is applied to terminals A, B, of magnitude and sign depending upon the deviation. This is rectified, in demodulator 23, to give a D. C. Voltage Whose magnitude and sign is dependent upon the magnitude and sense of the deviation. The D. C. when applied to winding it, produces differential variation of the impedances between terminal 5! and 52 respectively and terminal 2, so that a voltage is developed across the secondary winding i of transformer The connections are so arranged that this voltage is in such a sense as to oppose variation in the voltage between terminals lill, W2.

It will be seen that by adjustment of resistor 2| the level of the output voltage can be adjusted; and it will be appreciated that in certain circumstances it may be convenient to connect bridge it directly across terminals lili, I02. When however a transformer such as M5 is used it will usually be convenient to obtain the carrier input to demodulator 23 from a further secondary winding on transformer 29.

In Figure 2 is shown a modification for part of the circuit which may be connected between lines lili, I62 in place of transformer 29 and the bridge l8 shown in Figure 1, terminals A, B, in

4 Figure 2 being connected to the input terminals A, B of demodulator 23.

The circuit in Figure 2 comprises a bridge con s sting of resistors 4i, and inductors s3, 44. Inductor has an inductance substantially independent of the voltage to be app-lied to it, while that of inductor is rapidly decreases as the voltage applied to it is increased through a critical value. This can be arranged by, for example, winding th inductor upon a core of material having a sharp knee in the BH curve. The components are so chosen that when the voltage between terminals lili, use has its desired datum value the bridge is balanced and the voltage across inductor $43 is in the neighbourhood of its critical value. increase of the voltage between terminal Hi i, Hi2 above the datum thus produces a voltage between terminals A, B of one phase and a decrease of the voltage between the terminals Nil, )2 produces a voltage of the other phase between terminals A, B. This voltage is utilized, as in the embodiment of Figure l, to produce a voltage across winding 4 to counteract variations in the output voltage.

In Figure 3 is shown a further modification, which may be connected between terminals [ill and M2, replacing transformer 29, bridge i 8 and demodulator 23 of Figure 1, and enabling transformer 24 to be omitted.

The circuit of Figure 3 consists of a resistor in series with a bridge-connected dry plate rectifier and a tapped inductor 46 in series with a further dry plate rectifier 48. The inductor is of a similar kind to inductor it (Figure 2) but such that the critical voltage (which can be varied by adjusting the tap) is substantially equal to the desired output Voltage.

Terminals C, D of rectifier t? are connected to winding it (Figure 1) while terminals E, F are connected to winding id. The D. C. fluxes produced by the currents in windings i and iii are in opposition, and resistor is is such that when the output voltage between terminals lill, I 02 is at the desired datum the resultant fiux is zero. If the voltage varies from the datum the circuit acts, as described earlier to produce a voltage across winding to counteract the variation.

t will be appreciated that the devices shown in Figure 2 or 3 may be connected across lines lill, I92 through a transformer instead of directly if this is convenient.

I claim:

1. A voltage regulator supplying at a pair of output terminals a voltage of a substantially constant datum amplitude derived from a voltage of variable amplitude at a pair of input terminals comprising means connected across the output terminals to give a D. C. magnetic flux whose magnitude and sign are in accordance with the variation of the voltage across the output terminals from its datum amplitude, a trans former whose secondary winding is connected in series between the first input terminal and the first output terminal, said transformer having a centre-tapped primary, the centre tap of said primary being connected to one of the input terminals, two similar variable impedance elements of the saturable reactor type connected respec tively between the other input terminal and the remaining terminals of the transformer primary and means to vary the impedances of the variable impedance elements differentially in accordance with the aforementioned D. C. magnetic flux, the variation being such that the voltage across the transformer secondary is such as to reduce the variation of the voltage between the output terminals from its datum amplitude.

2. A voltage regulator as claimed in claim 1 wherein the means for deriving the D. C. flux comprise a bridge the impedance of at least one of whose arms depends upon the voltage across it, one pair of opposite terminals of the said bridge being connected across the output terminals of the regulator and the voltage across the remaining (output) pair of terminals being utilised to generate the requisite flux.

3. A voltage regulator as claimed in claim 2 wherein two opposite arms of the bridge consists of resistive elements whose resistance is largely independent of the current flowing therein while the remaining arms consist of resistive elements whose resistance varies substantially with the current flowing therein.

4. A voltage regulator as claimed in claim 3 wherein the resistive elements of substantially varying resistance are constituted by metal filament lamps.

5. A voltage regulator as claimed in claim 2 wherein the one pair of adjacent arms of the bridge consists of resistive elements while the other adjacent arms consist respectively of an inductor whose impedance is substantially independent of the voltage across it and an inductor whose impedance changes relatively suddenly at a critical value of the voltage across it.

6. A voltage regulator as claimed in claim 2 wherein one of the elements of the bridge is in- 6 dependently variable to enable the datum amplitude to be adjusted.

'7. A voltage regulator as claimed in claim 1 wherein the means for deriving a D. C. flux comprise a first impedance element whose impedance is substantially independent of the voltage across it in series with a first rectifier connected across the output terminals a second impedance element whose impedance varies substantially with the voltage across it in series with a second rectifier also connected across the output terminals with first and second windings respectively connected to the output of said rectifiers and arranged to generate the requisite flux.

8. A voltage regulator as claimed in claim 7 wherein the second impedance is constituted by an inductor whose impedance changes relatively suddenly at a critical value of the voltage across it 9. A voltage regulator as claimed in claim 2 comprising also a phase-sensitive demodulator, the input to which is supplied by the output from the bridge and the direct current output from which is applied to control the impedances of the saturable reactors.

FREDERICK ROGER MILSOM.

Name Date Ahlen July 24, 1951 Number 

